Could global warming increase wind shear over the Atlantic, potentially leading to a decrease in the frequency of Atlantic hurricanes? There is a growing consensus among hurricane scientists that this is indeed quite possible. Two recent studies, by Zhao et al. (2009), "Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM", and by Knutson et al. (2008), "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", found that global warming might increase wind shear over the Atlantic by the end of the century, resulting in a decrease in the number of Atlantic hurricanes. For example, the second study took 18 relatively coarse (>60 km grid size) models used to formulate the 2007 IPCC climate report, and "downscaled" them using a higher-resolution (18 km grid size) model called ZETAC that was able to successfully simulate the frequencies of hurricanes over the past 50 years. When the 18 km ZETAC model was driven using the climate conditions we expect in 2100, as output by the 18 IPCC models, the authors found that a reduction of Atlantic tropical storms by 27% and hurricanes by 18% by the end of the century resulted. An important reason that their model predicted a decrease in the frequency of Atlantic hurricanes was due to a predicted increase in wind shear. As I explain in my wind shear tutorial, a large change of wind speed with height over a hurricane creates a shearing force that tends to tear the storm apart. The amount of wind shear is critical in determining whether a hurricane can form or survive.

Figure 1. Top: predicted change by 2100 in wind shear (in meters per second per degree C of warming--multiply by two to get mph) as predicted by summing the predictions of 18 climate models. Bottom: The number of models that predict the effect shown in the top image. The dots show the locations where tropical storms formed between 1981-2005. The box indicates a region of frequent hurricane formation where wind shear is not predicted to change much. Image credit: Geophysical Research Letters, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", by Vecchi and Soden, 2007.

Since the Knutson et al. study using the 18 km resolution ZETAC model was not detailed enough to look at what might happen to major Category 3 and stronger hurricanes, a new study using a higher resolution model was needed. This was done by a team of modelers led by Dr. Morris Bender of NOAA's GFDL laboratory, who published their results in Science in February. The authors used the GFDL hurricane model--the model that has been our best-performing operation hurricane track forecasting model over the past five years--to perform their study. The GFDL hurricane model runs at a resolution of 9 km, which is detailed enough to make accurate simulations of major hurricanes. The researchers did a double downscaling study, where they first took the forecast atmospheric and oceanic conditions at generated by the coarse (>60 km grid) IPCC models, used these data to initialize the finer resolution 18 km ZETAC model, then used the output from the ZETAC model to initialize the high-resolution GFDL hurricane model. The final results of this "double downscaling" study suggest that although the total number of hurricanes is expected to decrease by the end of the century, we should expect an increase of 81% in the number of Category 4 and 5 storms in the Atlantic. This trend should not be clearly detectable until about 60 years from now, given a scenario in which CO2 doubles by 2100. The authors say that their model predicts that there should already have been a 20% increase in the number of Category 4 and 5 storms since the 1940s, given the approximate 0.5°C warming of the tropical Atlantic during that period. This trend is too small to be detectable, given the high natural variability and the difficulty we've had accurately measuring the exact strength of intense hurricanes before the 1980s.The region of the Atlantic expected to see the greatest increase in Category 4 and 5 storms by the year 2100 is over the Bahama Islands (Figure 2), since wind shear is not expected to increase in this region, and sea surface temperatures and atmospheric instability are expected to increase there.

The net effect of a decrease in total number of hurricanes but an increase in the strongest hurricanes should cause an increase in U.S. hurricane damages of about 30% by the end of the century, the authors compute, assuming that hurricane damages behave as they did during the past century. Over the past century, Category 4 and 5 hurricanes made up only 6% of all U.S. landfalls, but accounted for 48% of all U.S. damage (if normalized to account for increases in U.S. population and wealth, Pielke et al., 2008.)

Figure 2. Expected change in Atlantic Category 4 and 5 hurricanes per decade expected by the year 2100, according to the Science paper by Bender et al. (2010).

CommentaryThese results seem reasonable, since the models in question have been successfully been able to simulate the behavior of hurricanes over the past 50 years. However, the uncertainties are high and lot more research needs to be done before we can be confident of the results. Not all of the IPCC models predict an increase in wind shear over the tropical Atlantic by 2100, so the increase in Category 4 and 5 hurricanes could be much greater. Also, the GFDL model was observed to under-predict the strength of intense hurricanes in the current climate, so it may not be creating enough Category 4 and 5 hurricanes in the future climate of 2100. On the other hand, IPCC models such as the UKMO-HadCM3 predict a very large increase in wind shear, leading to a drastic reduction in all hurricanes in the Atlantic by 2100, including Category 4 and 5 storms. So Category 4 and 5 hurricane frequency could easily be much greater or much less than the 81% increase by 2100 found by Bender et al.

The estimates of a 30% increase in hurricane damages by 2100 may be considerably too low, since this estimate assumes that sea level rise will continue at the same pace as was observed in the 20th century. Sea level rise has accelerated since the 1990s, and it is likely that this century we will see much more than than the 7 inches of global sea level rise that was observed last century. Higher sea level rise rates will sharply increase the damages due to storm surge, which account for a large amount of the damage from intense Category 4 and 5 hurricanes.

Keep in mind that while a 30% in hurricane damage by the end of the century is significant, this will not be the main reason hurricane damages will increase this century. Hurricane damages are currently doubling every ten years, according to Pielke et al., 2008. This is primarily due to the increasing population along the coast and increased wealth of the population. The authors theorize that the Great Miami Hurricane of 1926, a Category 4 monster that made a direct hit on Miami Beach, would have caused about $150 billion in damage had it hit in 2005. By 2015, the authors expect the same hurricane would do $300 billion in damage. This number would increase to $600 billion by 2025 (though I think it is likely that the recent recession may delay this damage total a few years into the future.) It is essential that we limit coastal development in vulnerable coastal areas, particularly along barrier islands, to reduce some of the astronomical price tags hurricanes are going to be causing. Adoption and enforcement of strict building standards is also a must.

The authors of the GFDL hurricane model study have put together a nice web page with links to the paper and some detailed non-technical explanations of the paper.

Quoting CycloneOz:It's a little bit funny, when you get bannedHow you get back in, we do not understandI'm not a WU admin, but if I wasI'd IP you out so hard, your head would buzz

I've tried to ignore you, but you defeat me againNow I'm ready to stab myself in the head with a penYou're back one more time and I feel myself heaveNo matter what you call yourself now, you're still JFV

And you can tell everybody, it's really not youSome may believe, but I'm not a foolI know it's you, manI know it's you, man...we sniff you out like a dogHow wonderful life is, when you're not on the blog

Quoting Tropicsweatherpr:Good morning. TSR released today its April outlook and raises the numbers from the December ones now up to=16/9/4.

Link

It's no surprise as to where everyone is heading this year in terms of forcasting a very active season based upon current conditions with "heat" and ssts being a major positive factor. When all is said and done (the SSTs wiil be there and perhaps earlier than we think), I think the major factor to watch this year will be sheer levels (along with a pre-existing disturbance)......Absent some major currently unforseen issues that may arise in the Summer (i.e. a major SAL outbreak during the heart of the CV season or volcanic ash eruption), I think that overall sheer levels will determine the start and end of this year's season.

Good Morning from Tallahasse.....Front came through yesterday, no major problems, and nice cool morning and gorgeous weather for the weekend and through this entire upcoming week in these parts....Life, weather wise, is good right now.

Yeah I Love Ron White, he is quite vulgar, but funny. Anywho if you see this post before it gets too far in the depths of the blog, welcome alex..Great minds at work here, you will learn alot about weather, climate, and of course the star of the show in my opinion, tropical cyclones. You will find i don't post on here hardly at all i am a lurker who feeds off everyone's intellect ...lol

For this upcoming hurricane season all the information that has been put together by levi, sormW, and drakoen i think we will have an interesting year full of landfalls and storms. im going with 16 storms with 8 being hurricanes and 4 majors but there is a lot of uncertainty still because even though el nino is going going gone this year i think there will still be effects at the onset of the season but by the last week of june i think will have our first tropical system and then its off to the races for the rest of the season. Remember this is my very amatuerish opinion so please if anyone wants to say where i am wrong by all means tell me i want to understand enso and the way it affects hurricane seasons.

Mornin' all. I've been reading the series on Katrina's storm surge and now I am interested in storm surge potential for my area. It seems like about 1/4 of New Providence island, specifically along the SE coast, would be vulnerable to anywhere from 6 to 16 feet of surge in a cat 5.... I guess worst case would be with a storm passing over, or just south of the island from the SE.... which is not that unusual a direction from which to see a storm approach. In fact, if Ike had stuck to its original path, we would likely have had factual data as to the effects of a cat 4 on the NP coast.

Looks like where getting rain this morning in the tampa area but by the time we wake up the rain will be gone and temps in the 80s tomorrow but will cool down afterwards thats good news i like cold weather.

Cool Cane 2010 and dont worry about it some people always think a new user is jfv hes like the boogeyman of the blog so if someone calls you out again just ignore them and talk weather isnt that why were on here in the first place?

Quoting alexhurricane1991:Hello everyone! im alexhurricane1991 and this is my first post ever on this blog. ive been reading this blog for 5 years and i found that this site has some of the best minds on the internet about hurricanes. I live in tampa and i am a weather fanatic ever sense i was 3 and im 18 now and in the not to distant future going to join the navy to become a meteorologist for them so i cant wait to put my two cents in these sometimes intriguing conversations on this blog!

Hello everyone! im alexhurricane1991 and this is my first post ever on this blog. ive been reading this blog for 5 years and i found that this site has some of the best minds on the internet about hurricanes. I live in tampa and i am a weather fanatic ever sense i was 3 and im 18 now and in the not to distant future going to join the navy to become a meteorologist for them so i cant wait to put my two cents in these sometimes intriguing conversations on this blog!

Quoting Cane2010:Thanks, I don't even know who he or she is. I just got defensive taht way, because I do not like people bluntly attacking me taht way, you know? Who would??? LOL. Anyways, if I did insult anyone in here, I sincerely apologies, :(.

Quoting Cane2010:Thanks, I don't even know who he or she is. I just got defensive taht way, because I do not like people bluntly attacking me taht way, you know? Who would??? LOL. Anyways, if I did insult anyone in here, I sincerely apologies, :(.

Quoting StSimonsIslandGAGuy:Yeah I don't think cane2010 is JFV. I never saw JFV get that mean. (although he could have been and I missed it) I think it is someone else. Who's been banned even more than JFV has been.